Former Wildlife Services employees estimate that these numbers are likely hugely short of the actual numbers.

According to the Center for Biodiversity, the century-old Wildlife Services was created in 1915 to eliminate invasive species that weaken the livestock and agricultural sector. But for the past years, the agency had been highly criticized because it targets even innocent animals, including pets.

It has reportedly killed 32 million native animals since 1996.

The killings destroy the balance of nature as many of the species they kill are at the top of the food chain, making them beneficial to the health of ecosystem.

"It is a tragedy that our government continues to needlessly slaughter America's wildlife year to year," said Kelly Nokes, carnivore campaign lead for WildEarth Guardians. "Wildlife Services' cruel killing of native animals is based on disproven anti-wildlife bias and undermines the critical natural systems upon which we all depend."

The program uses inhumane ways to kill; some of which include the use of cruel tools, including trapping, poisoning and shooting from airplanes.

"There's simply no scientific basis for continuing to shoot, poison and strangle millions of animals every year-a cruel practice that not only fails to effectively manage targeted wildlife but poses an ongoing threat to other animals, including pets," Michael Robinson of the Center for Biological Diversity told EcoWatch.